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UC 12 12th Users Conference on BiAxial Fatigue Testing

November 11th, 2015

Robert Keplin M.Sc. Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF www.lbf.fraunhofer.de

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LOAD FILE DEVELOPMENT

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Content

Load file fundamentals

Specification of a load file

Basic load file development process

Load file development for 3 axle semi-trailer application

Used wheel end instrumented with strain gauges

Local strain measurements for transformation of wheel loads to test rig loads

Process for load file development of used wheel end

Summary

Outlook

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Specification of a load file for a LBF BiAxial fatigue test machine LBF load file is specified by:

Combination of different actuator load sequences (vertical and lateral direction) in kN

Defined drum speed for each load sequence in km/h

Defined length of time for each load sequence in sec

By means of a test load file a correct correlation between the LBF design spectrum and the BiAxial time reduced test spectrum shall be given in terms of loading, stress and damage content

Seq Fv Fh v t[kN] [kN] [km/h] [sec]

1 37.5 0.00 73 18.02 50.0 27.50 73 6.03 25.0 7.50 73 15.04 37.5 0.00 73 43.55 62.5 29.00 73 6.0

98 45.0 21.00 73 2.099 37.5 0.00 73 30.1

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Basic load file development process (I)

Results of experimental stress analysis on LBF flat track are input for the load file development

Load assumptions

Determination of local peak stresses by measurements of local strains on LBF flat track

Derivation of the LBF design spectrum and calculation of RFS values − Required Fatigue Strength − for the relevant locations

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Basic load file development process (II)

Transformation of wheel loads to test rig loads by means of damage accumulation on the basis of local strain measurements in BiAxial test rig

Accurately stress reproduction for all design load cases

Measurements of local strains in BiAxial test rig for complete period of load sequences

Comparison of measured BiAxial test spectrum to LBF design spectrum via RFS value concept

Load file / load sequence adjustment until required analogy is given in terms of damage content

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Test duration for heavy duty truck application − front axle

Steel wheels and cast-iron hubs: 16,000 km

Basic Design Spectrum for 500,000 km of Service and Test Spectrum for heavy duty trucks (front axle)

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Load file development for 3 axle semi-trailer application

Seq Fv Fh v t[kN] [kN] [km/h] [sec]

1 37.5 0.00 73 18.02 50.0 27.50 73 6.03 25.0 7.50 73 15.04 37.5 0.00 73 43.55 62.5 29.00 73 6.0

98 45.0 21.00 73 2.099 37.5 0.00 73 30.1

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Wheel end for 3 axle semi-trailer − European usage

11.75x22.5 inset120 steel wheel typical semi-trailer wheel for European usage

Rated wheel load: 4.500 kg

Tire size: 385/65 R 22.5

No. of studs: 10

Pitch circle: ø335 mm

Stud hole diameter: ø26 mm

No. of ventilation holes: 10 aligned to area between stud hole center

Ventilation hole design: oval

Valve hole: aligned to ventilation hole center

mating flange thickness: ca. 13 mm

Hub system w/ brake disk typical semi-trailer hub system for European usage

Rated wheel load: 4.500 kg

Hub system consist of:

Hub flange (cylindrical | cast-iron)

Brake disk

Hub-unit

No. of studs / stud size:10 / M22x1.5

Brake disk: screwed w/ wheel studs

Hub-unit: screwed w/ flange screws M18x1.5

No. of flange screws: 12

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SGs used at different locations on the wheel and the hub flange

Wheel end instrumented w/ strain gauges

exemplary cross section wheel

exemplary cross section wheel end

23 SGs on wheel 4 on wheel flange outside 2 on mating flange 3 on disc radius inside 4 on ventilation hole inside 3 on ventilation hole outside 2 close to welding line 1 close to valve hole 2 on drop center 1 on rim well 1 on inner rim flange

9 SGs on hub flange 3 on radius behind wheel bolt head inside 3 on radius wheel centering outside 2 on casting skin inside 1 on casting skin outside

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Most important SGs used for the measurement of local strains in LBF BiAxial test rig

Wheel end instrumented w/ strain gauges

exemplary cross section wheel

exemplary cross section wheel end

6 SGs on wheel 1 on wheel flange outside, close to

wheel nut contour (screwing area) 1 on mating flange, pretty close to

the hub flange contour 1 on ventilation hole inside

(peak stress area) 1 on ventilation hole outside 1 close to valve hole (rim well area) 1 on inner rim flange 2 SGs on hub flange

1 on radius wheel centering outside 1 on casting skin inside (close to wheel bolt head |

peak stress area)

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Local strain measurement w/ 8 channel telemetry system

Using of high-precision telemetry system by datatel for the wireless transmission of the measured strains

6 measuring channels used for wheel structure

2 measuring channels used for hub flange structure

Sample rate: 200 hz

Operable temperature range of transmitter: 0 to 85 °C

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BiAxial fatigue testing Realistic wheel loads while testing

Straight driving Cornering Rough road

Different actuator forces are needed for generation of equivalent wheel forces/local stresses by tilting and running against sidewalls of inner drum system

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-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70

Vert

ical

whe

el lo

ad [k

N]

Lateral wheel load [kN]

Design load cases

Transformation of wheel loads to test rig loads Accurately stress reproduction for design load cases

Cornering

Actuator load combination

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Transformation of wheel loads to test rig loads Accurately stress reproduction − iteration loops

Many iteration loops needed until measured stresses are reproduced in an adequate way for all design load cases and each strain gauge

Inner rim flange

Ventilation hole inside

Mating flange inside

Ventilation hole outside

Wheel flange outside

Valve holeVertical Lateral

MPa in % MPa in % MPa in % MPa in % MPa in % MPa in % kN in % kN in %100 100 100 100 100 100 100 100

1. iteration 92,0 85,0 93,0 87,0 86,0 94,0 100,0 100,0

Relative deviation [%] -9,00 -15,00 -8,00 -13,00 -14,00 -7,00 0,00 0,00Absolute deviation [MPa] -12,00 25,00 -9,00 -20,00 -15,00 -6,00 0,00 0,00

2. iteration 95,0 92,0 96,0 93,0 93,0 96,0 105,0 110,0

Relative deviation [%] -5,00 -8,00 -4,00 -7,00 -7,00 -4,00 5,00 10,00Absolute deviation [MPa] -7,00 -13,00 -5,00 -10,00 -8,00 -3,00 4,00 3,00

Strain gauges on wheel structure Design load case cornering

Stresses for design load case Wheel loads

Actuator loadsMeasured stresses

X. iteration 102,0 99,0 103,0 101,0 102,0 104,0 110,0 120,0

Relative deviation [%] 2,00 -1,00 3,00 1,00 2,00 4,00 10,00 20,00Absolute deviation [MPa] 3,00 -2,00 4,00 2,00 3,00 3,00 8,00 6,00

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Final load file development − Transformation of wheel loads to test rig loads by means of damage accumulation

Damage accumulation

Analysis: BiAxial test spectrum vs. LBF design spectrum

Load file development/ adjustment until required analogy is given in terms of damage content

Measurements of local strains on BiAxial test rig for complete period of load sequences

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Developing of an adequate wheel load file for 3 axle semi-trailer application

Specification of the wheel test load file

Test load file consists of 99 load sequences

Driven distance of one period − 99 load sequences: ca. 65 km

Test duration: 16,000 km − ca. 246 repetitions

Matched to a drum speed of 73 km/h and an inner drum size of 1.8 m

Load sequences mixed for good drivability

Cover new LBF design spectrum for 3 axle semi-trailer application (500,000 km) in a good way Seq Fv Fh v t

[kN] [kN] [km/h] [sec]1 37.5 0.00 73 18.02 50.0 27.50 73 6.03 25.0 7.50 73 15.04 37.5 0.00 73 43.55 62.5 29.00 73 6.0

98 45.0 21.00 73 2.099 37.5 0.00 73 30.1

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Inner rim flange Ventilation holeinside

Mating flange inside Ventilation holeoutside

Wheel flange outside Valve hole

RFS

valu

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RFS LBF design Spectrum RFS Load File Semi-Trailer

Results overview Load file adjustment by means of RFS value concept

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LBF design spectrum vs. test spectrum Strain gauge on ventilation hole inside

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Inner rim flange Ventilation holeinside

Mating flange inside Ventilation holeoutside

Wheel flange outside Valve hole

RFS

valu

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RFS Load File Front Axle [16,000 km] RFS Load File Semi-Trailer [16,000 km]

Load file comparison by means of RFS value concept Load file front axle vs. new load file semi-trailer

+2%

+3%

+4%

+1%

+7%

+1%

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Summary Up to now an adequate wheel test load file has been developed for typical

11.75x22.5 IS120 steel wheels for 3 axle semi-trailer application

New load file for trailer axle application is in all relevant locations of the wheel structure more severe than the basic load file for front axle application, especially in the wheel screwing area

Validity for hub:

There is a deviation between the wheel and the hub due to the different lateral load transmission on BiAxial test rig for the hub higher actuator loads are necessary

According to the current load file status the RFS value for the most critical location is about 6% too low extended test duration is needed

Validity for aluminum wheels:

Until now not enough measurements have been done for verification of the load file for aluminum wheels

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Outlook Current load file, which is valid for steel wheels, will be most likely available in

the final version within 1. Quarter 2016

Outlook for hub

More measurements still need to be done for final conclusion

According to current status mixed test strategy could solve the deviation between wheel and hub e. g. test the wheel at first and continue hub testing w/ increased test parameters (cv and ch)

Outlook for aluminum wheels

With SGs instrumented typical 11.75x22.5 IS120 aluminum wheel as well an accurate regression model is already available

More measurements still needed for final validation

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… we will keep your wheels running

Thank you for your attention.